1. Field of the Invention
This invention relates to a packaging apparatus for packaging each of successively supplied articles in a bag of a heat-meltable, heat-shrinkable film, and more particularly to an improved packaging apparatus capable of providing a packaged article which is excellent in appearance and thus high in commercial value.
Throughout the specification, the term "tube (or tubular)" is used to refer to an elongate hollow body or column which may be optional (circular, oval, rectangular, etc.) in cross section. The term "tube" is also used as a verb meaning an act of forming a film or sheet into a tubular shape.
2. Description of the Prior Art
In packaging each of successively supplied articles by an enclosure made of a heat-meltable, heat-shrinkable film, it is a common practice to first form a continuous length of such film into a tube surrounding the article with both longitudinal margins of the film heat-sealed together. Then, the film tube thus formed is transversely heat-sealed and cut at two positions slightly ahead of and behind the article to provide a film bag completely enclosing the article. Finally, the film bag is subjected to hot air treatment, whereby the film bag comes into contact with the article inside.
An apparatus usable for the above packaging operation is disclosed for example in Japanese Utility Model Application Laid-open No. 57-13401 (Laid-open: Jan. 23, 1982; Application No.: 55-91204; Filed: June 28, 1980; Applicant: Kabushiki Kaisha Fuji Kikai Seisakusho; Inventor: Mamoru Ichikawa).
The packaging apparatus according to the above laid-open application incorporates a longitudinal sealer comprising a pair of heated discs each having a flat circumferential surface. A certain width of overlapping longitudinal margins of a tubed film are nipped between the circumferential surfaces of the heated discs and heat-sealed together.
The packaging apparatus of the above laid-open application further incorporates a transverse sealer which comprises a pair of synchronously rotated rotary shafts arranged behind the longitudinal sealer and extending transversely of the tubed film respectively thereabove and therebelow, and a pair of heated sealer bodies respectively mounted on the pair of rotary shafts. Each sealer body has an arcuate sealing surface which comes into contact with a certain width (corresponding to the circumferential length of the arcuate contact surface) of the tubed film for transverse heat-sealing thereof upon every single turn of the respective rotary shafts. One of the sealer bodies is provided with a central cutter blade having a sharp cutting edge projecting beyond the arcuate sealing surface, so that the tubed film is transversely cut at the center of each transversely sealed portion of the tubed film to provide a film bag completely enclosing each article.
It is obvious from the foregoing description that the film bag provided by the packaging apparatus of the above laid-open application inevitably has relatively wide sealed portions (both longitudinal and transverse) which constitute unacceptable projections on the final product upon subsequent shrinkage of the film bag. In addition to being detrimental in appearance and handling of the product, such projections can sometimes hide informative printings on the article inside the film bag and thereby reduces the commercial value of the product.
Japanese Utility Model Publication No. 61-26037 (Published: Aug. 5, 1986; Application No.: 55-61070; Filed: May 2, 1980; Applicant: Tokiwa Kogyo Co. Ltd.; Inventor: Yoichiro Kimoto) discloses another type of transverse sealer which comprises a pair of synchronously rotated rotary shafts extending transversely of a tubed film respectively thereabove and therebelow, a pair of heated sealer bodies respectively mounted to the pair of rotary shafts, a cutter blade mounted to one of the sealer bodies and having a rounded cutting edge, a counter blade having a flat contact surface, and a pair of presser rods respectively disposed ahead of and behind the cutter blade. The rounded cutting edge of the cutter blade substantially comes into line contact with the flat contact surface of the counter blade upon every single turn of the respective rotary shafts to transversely heat-seal the tubed film interposed between the two blades. The presser rods press and tension the tubed film when the film is heat-sealed, so that the tubed film is cut at the rounded cutting edge which itself provides no cutting function without tensioning of the film because of its roundness.
Each transverse seal portion or line obtained by such transverse sealer is extremely narrow and thus almost negligible in appearance of the final product.
This laid-open Japanese application, however, fails to disclose a longitudinal sealer which is capable of forming a narrow longitudinal seal line.